There is a range of materials that have been used in the past and present to help during the mining reclamation and rehabilitation process to seal in potential contaminants, with varying degrees of success. However, given the extensive focus on environmental stewardship today, it's vital that you use the right solution for your site's contamination and geological concerns. This can include issues such as settling due to limestone base material, seismic or volcanic activity, agricultural activity, and similar factors. Make sure that you're making the right choice for your situation before simply going with what is inexpensive or traditional.
Compacted Clay
A century ago, or even less, manmade liners were practically unheard of in the mining industry. Instead of using manmade materials, a common source of liners and sealants was simply compacted clay which had been brought in from local sources. These types of liners are constructed instead of being installed. It requires a long, difficult construction process, including preparing a foundation, perfecting the clay's moisture content, placing the materials, and then compaction, so that air pockets, potential faults, or cracks are sealed. The moisture content of the clay must be maintained perfectly until water is added to cover the clay because drying the clay can cause it to crack, shrink and form other leakage issues. These issues also make this type of liner vulnerable to earthquakes and similar seismic activity, as well as settlement across the foundation, which can cause cracks. Clay can also contain material that will interact with some leach solutions, which can weaken the seal and cause a failure, unlike geosynthetic liners. Repairing a damaged compacted clay liner, even if faults are found in a timely manner, can be very difficult if not utterly impossible.
Geosynthetic Clay
Geosynthetic clay liners manage the difference between traditional clay liners and geomembranes. It has bentonite clay which is then sandwiched in between two layers of geosynthetic materials. When exposed to water, the bentonite absorbs the water, expanding up to 30 times its original volume. This forms a gel that prevents liquid from passing through it. The gel helps the liner be less vulnerable to shifting or settling and will do a certain amount of self-repair, but because the bentonite is between the layers, abrasions, and punctures to the geomembrane can cause the material to leak, which should be taken into careful consideration before using this material, as it will be difficult to impossible to repair without a significant investment of time and money.
Geomembranes
Geomembranes provide a solid option by adapting to the changing environment, to a certain extent, such as shifting and settling. Although, how well it adapts will depend on the specific geomembrane you select. During the mine's lifespan, it's important to consider the different roles the geomembrane will play over time. Instead of using one geomembrane at one point and then replacing it with another material later on during the reclamation and rehabilitation process, why not find a single geomembrane that will handle the entire process? This helps prevent waste and extra work from having to take place during the closure process. After using a geomembrane has been employed as a bottom liner, you can then use it to cap and seal the reclaimed mine, creating a sealed envelope around all contamination.
Uses for Geomembranes in Mining Reclamation and Rehabilitation
Buried Liner Primary Containment
Implementing a geomembrane as the buried liner for the bottom of your layer or catchment basement, provides your first defense against soil contamination. If you don't have an impermeable layer below your mining storage pond, you can discover that you've caused extensive damage to the environment as mining chemicals and heavy metals seep into the soil. If you can contain these compounds from the beginning, remediation is much faster and less expensive than it would be otherwise. If your system is older and using compacted clay or a similar approach, consider installing a liner immediately to prevent further damage in the future. This is especially important because as ponds and basins age, they are more likely to form additional seepage points and leaks.
Reliable Capping Option
Your geomembrane can keep water and vapors from seeping up as well; whether from a tailings pile, storage pond, or reclamation site. Vapors, especially, are able to escape compacted clay liners or layers of soil. It also provides you with an opportunity to recycle your existing liner, by taking the liner that had been below your mining operation and placing it as a cap on top to prevent surface water from leaching toxins from your mining site into the groundwater. For outstanding containment, use the same polymer on both the top and bottom, then seal the two layers together. Regardless of whether you're planning on adding other materials to your cap, a geomembrane layer will provide the best possible performance and optimal containment.
Complete Infiltration Control
Because geomembranes are impermeable, they protect your mining operation's potential contaminants from escaping from water coming in from above or below. This is especially important when you're mining in an area with a high water table. This helps you avoid unintentional groundwater contamination or runoff problems. Similarly, capping your ponds with an impermeable geomembrane prevents rainwater and floodwater from entering the top of your pond or tailings piles, keeping this excess water from becoming a runoff problem that can potentially contaminate area waterways.
Basis for Revegetation
As one of the best options for reclamation and rehabilitation of a damaged mining site, revegetation is a powerful tool. However, that doesn't mean you shouldn’t use a geomembrane as part of your overall plan. You can easily design a capping system that integrates both geomembranes and living materials to attain a long-lasting, useful reclamation and rehabilitation process. You may need to add a deeper layer of topsoil over the geomembrane to account for possible root growth, but by carefully selecting the plants you incorporate, you can still work even with a shallow soil layer. Mines that have been replanted with vegetation tend to recover in a shorter period of time while functioning better for recreation or housing construction than non-planted options.
Combining Geosynthetic Layers
Mining reclamation and rehabilitation projects will typically involve multiple types of geosynthetic layers beyond geomembranes. Though geomembranes are a good, impermeable layer for controlling the flow of water, there may be other options to consider for capping or sealing. For example, geosynthetic clay liners can be used in combination with geomembranes to help reinforce loose soils that are located below or above the mineral deposits being mined. For loose or steep sides, geotextiles are commonly used to prevent the sides from collapsing after filling or covering, as they allow plant matter to grow through and provide additional securement of the soils. Extruded or nonwoven matted geofabrics can be used as underlayment below geomembranes in rough soil or to prevent the formation of small voids in loose soil. Consider all of your needs and how your different geosynthetics will work together throughout the entire life cycle of the mine.
Seam Strength
The liner under your mine reclamation and rehabilitation projects can come under a lot of stress while your fill material is being introduced and heavy equipment is being used on top of it. Adding material to a weak liner can cause the bottom layers to tear, resulting in leaks into the soil. To protect the soil and water table located underneath your reclamation site, you'll need to protect your original liners. By starting with strong seams at the beginning of the process and choosing the proper geomembrane materials, you'll be able to successfully reclaim the mine years later because you'll already have strong seams in place. One of the best ways to avoid stress leaks over time is by ordering a liner fabricated specifically for the demands of your mining site.
By choosing the right mining geomembranes for each stage of your mining process, you can get the most out of your mining reclamation and rehabilitation project without wasting money, time, and effort. Whether you need to add a new bottom liner to your existing site or want to finish your cap to create a solid foundation for your rehabilitation project, we have everything you need. At BTL Liners, we've been in the geomembrane innovation sphere since the start and take our commitment to provide the best products very seriously.
